1. Field of the Invention
The invention relates to a method for producing plastic products, more particularly to a method for producing plastic products which comprises improvements with respect to the heat-sealing of the plastic products.
2. Description of the Related Art
Conventionally, plastic products, such as inflatable cushions, air beds, floats, etc. are fabricated by joining a plurality of plastic sheet parts along the peripheries of the same. As shown in FIG. 1, the joined portions 10, 20 of the sheet parts 1,2 of a plastic article are heated and pressed during a heat-sealing process to form connecting seams of a plastic product. Since the thickness of the heat-sealed seams is decreased, the structural strength at the seams of the plastic product is relatively weak.
In addition, to maintain a plastic product, such as an infaltable cushion pad 3, in a generally cubic configuration, connection members 31 are provided within the interior of the cushion pad 3, as shown in FIG. 2. The two ends of the connection members 31 are connected to two opposed face sheets 30 of the cushion pad 3 during a heat-sealing process. Since the thickness of the face sheets 30 at the joints of the connection members 31 and the face sheets 30 are decreased due to the heat-sealing process, the joints on the cushion pad 3 are liable to be damaged when in use.
In order to address the aforesaid problems encountered with the heat-sealed joints of the conventional inflatable articles, a solution therefor is to use thick face sheets in fabricating products. However, this increases the costs of manufacturing such inflatable products.
U.S. Pat. No. 3,959,052 discloses a method for preparing a wraparound closure for cables, pipes, splices, and junctions to effect repair, insulation, or waterproofing. The method includes overlapping and sealing two thick edges of a sheet to form a tubular member around an item to be wrapped. The sheet is made of a heat shrinkable plastic material. The two ends of the sheet are clamped and the material between the clamped edges is stretched and cooled below the crystalline melting point of the material while it is still in expanded condition. The resulting sheet thus has a stretched central section which is heat shrinkable or heat recoverable, and two thick ends which are not stretched. These thick ends are not formed intentionally for reinforcing the sealed joint of the two ends of the sheet. Rather, they are formed inherently when they are clamped during the stretching process of the sheet. In addition, the method in this patent provides only two thick ends where the sheet is clamped. This patent does not contemplate reinforcing the heat-sealed joints of plastic products by thickening parts of a sheet and suggests nothing relevant to the thickening of a sheet in regions between two ends of the sheet.